Methods and Apparatus for Performing Spine Surgery

ABSTRACT

Systems and methods are described for correcting sagittal imbalance in a spine including instruments for performing the controlled release of the anterior longitudinal ligament through a lateral access corridor and hyper-lordotic lateral implants.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/702,685 filed on Sep. 12, 2017, which is a continuation of U.S.patent application Ser. No. 14/918,137 filed Dec. 19, 2014 (now U.S.Pat. No. 9,757,246), which is a continuation of U.S. patent applicationSer. No. 14/578,215 filed Dec. 19, 2014 (now U.S. Pat. No. 9,192,482),which is a continuation of U.S. patent application Ser. No. 13/653,335filed Oct. 16, 2012 (now U.S. Pat. No. 8,920,500), which is acontinuation of U.S. patent application Ser. No. 12/799,021 filed Apr.16, 2010 (now U.S. Pat. No. 8,287,597), which claims the benefit ofpriority from U.S. Provisional Patent Application Ser. No. 61/212,921filed Apr. 16, 2009, and U.S. Provisional Patent Application Ser. No.61/319,823 filed Mar. 31, 2010, the entire contents of which is herebyexpressly incorporated by reference into this disclosure as if set forthin its entirety herein.

FIELD

The present invention relates to implants and methods for adjustingsagittal imbalance of a spine.

BACKGROUND

A human spine has three main regions—the cervical, thoracic, and lumbarregions. In a normal spine, the cervical and lumbar regions have alordotic (backward) curvature, while the thoracic region has a kyphotic(forward) curvature. Such a disposition of the curvatures gives a normalspine an S-shape. Sagittal imbalance is a condition in which the normalalignment of the spine is disrupted in the sagittal plane causing adeformation of the spinal curvature. One example of such a deformity is“flat-back” syndrome, wherein the lumbar region of the spine isgenerally linear rather than curved. A more extreme example has thelumbar region of the spine exhibiting a kyphotic curvature such that thespine has an overall C-shape, rather than an S-shape. Sagittal imbalancecan be a problem in that it is biomechanically disadvantageous andgenerally results in discomfort, pain, and an awkward appearance in thatthe patient tends to be bent forward excessively.

Various treatments for sagittal imbalance are known in the art. Thesetreatments generally involve removing at least some bone from a vertebra(osteotomy) and sometimes removal of the entire vertebra(vertebrectomy), in order to reduce the posterior height of the spine inthe affected region and recreate lordotic curve. Such procedures aretraditionally performed via an open, posterior approach involving alarge incision (often to expose multiple spinal levels at the same time)and require stripping of the muscle tissue away from the bone. Theseprocedures can have the disadvantages of a large amount of blood loss,high risk, and a long and painful recovery for the patient. Furthermore,depending upon the patient, multiple procedures, involving both anteriorand posterior approaches to the spine, may be required.

The present invention is directed at overcoming, or at least improvingupon, the disadvantages of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is a lateral view representing a portion of a sagitallyimbalanced lumbar spine lacking the normal lordotic curvature;

FIG. 2 is a side view representing the lumbar spine of FIG. 1 afterrestoration of the lordotic curvature using a hyper-lordotic fusionimplant, according to one example embodiment;

FIG. 3 is a top down view depicting the creation of a lateral accesscorridor formed with surgical access system through the side of thepatient to the target disc space, according to one example embodiment;

FIG. 4 is a perspective view depicting a lateral access corridor formedwith a retractor assembly through the side of the patient to the targetdisc space, according to one example embodiment;

FIG. 5 is a front perspective view of an Anterior Longitudinal Ligament(ALL) resector for safely releasing the ALL through a lateral accesscorridor, according to one example embodiment;

FIG. 6 is an enlarged from perspective view of the distal portion of theALL resector of FIG. 5;

FIG. 7 is an enlarged side view of the distal portion of the ALLresector of FIG. 5;

FIG. 8 is an exploded front perspective view of the ALL resector of FIG.5;

FIG. 9 is a front perspective view of an ALL resector for safelyreleasing the ALL through a lateral access corridor, according toanother example embodiment;

FIG. 10 is a side view of the ALL resector of FIG. 9;

FIG. 11 is an enlarged side view of the distal end of the ALL resectorof FIG. 9;

FIG. 12 is an enlarged side view of the distal end of the ALL resectorof FIG. 9 having curved finger portions;

FIGS. 13-15 are anterior-front perspective, posterior-rear perspective,and front views of a hyper-lordotic lateral implant according to oneexample embodiment;

FIGS. 16-17 are posterior-rear perspective and rear views of ahyper-lordotic lateral implant according to another example embodiment;and

FIGS. 18-19 are posterior-rear perspective and rear views of ahyper-lordotic lateral implant according to still another exampleembodiment.

DESCRIPTION OF A PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. The methods and devices described herein include avariety of inventive features and components that warrant patentprotection, both individually and in combination.

With reference to FIGS. 1-2, devices and methods of the presentinvention are utilized to correct sagittal imbalance, including lumbarkyphosis, by increasing the anterior height of the affected spinal area(as opposed to reducing the posterior height). FIG. 1 illustrates aportion of the lumbar spine lacking the standard lordotic curvature. Tocorrect the sagittal imbalance, illustrated in FIG. 2, a hyper-lordoticimplant 10 is positioned into the disc space at the appropriate spinallevel (e.g. between V1 and V2). An anterior sidewall 12 ofhyper-lordotic implant 10 has a height significantly larger than anopposing posterior sidewall 14 such that when the implant is positionedwithin the disc space the anterior aspects of V1 and V2 are forced apartwhile the posterior aspects are not (or at least not to the samedegree), thus imparting a lordotic curvature into the spine. To allowthe anterior aspects of V1 and V2 to separate and receive thehyper-lordotic implant 10, the Anterior Longitudinal Ligament (ALL) thatruns along the anterior aspect of the spine may be released or cut (15).According to a preferred method, the implant 10 is implanted through alateral access corridor formed through the side of the patient.Accessing the targeted spinal site through the lateral access corridoravoids a number of disadvantages associated with posterior access (e.g.cutting through back musculature and possible need to reduce or cut awaypart of the posterior bony structures like lamina, facets, and spinousprocess) and anterior access (e.g. use of an access surgeon to movevarious organs and blood vessels out of the way in order to reach thetarget site). Accordingly, by accessing the target site via a lateralaccess approach and correcting the sagittal imbalance without reducingthe posterior height (i.e. no bone removal) the high blood loss andpainful recovery associated previous methods may be avoided (or at leastmitigated).

According to one example, the lateral access approach to the targetedspinal space may be performed according to the instruments and methodsdescribed in commonly owned U.S. Pat. No. 7,207,949 entitled “SurgicalAccess System and Related Methods,” and/or U.S. patent application Ser.No. 10/967,668 entitled “Surgical Access System and Related Methods,”the entire contents of which are each incorporated herein by referenceas if set forth herein in their entireties. With reference to FIGS. 3-4,a discussion of the lateral access instruments and methods is providedin brief detail. With the patient 20 positioned on their side, asurgical access system 20 is advanced through an incision 20, into theretroperitoneal space 22, and then through the psoas muscle 24 until thetargeted spinal site (e.g. the disc space between V1 and V2) is reached.The access system 26 may include at least one tissue dilator, andpreferably includes a sequential dilation system 28 with an initialdilator 30 and one or more additional dilators 32 of increasingdiameter, and a tissue retractor assembly 34. As will be appreciated,the initial dilator 30 is preferably advanced to the target site first,and then each of the additional dilators 32 of increasing diameter areadvanced in turn over the previous dilator. A k-wire (not shown) may beadvanced to the target site and docked in place (for example, byinserting the k-wire into the vertebral disc) prior to, in concurrencewith, or after advancing the initial dilator 30 to the target site. Withthe sequential dilation system 28 positioned adjacent the target site(and optionally docked in place via the k-wire), the retractor assembly34 is then advanced to the target site over the sequential dilationsystem 28. According to the embodiment shown, the retractor assembly 34includes retractor blades 36, 38, 40 and a body 42. With the sequentialdilation system 28 removed, the retractor blades 36, 38, and 40 areseparated (FIG. 5), providing the lateral access corridor through whichinstruments may be advanced to prepare the disc space and insert theimplant 10. According to one example, the posterior blade 36 may befixed in position relative to the spine prior to opening the retractorblades. This may be accomplished, for example by attaching a shim to theblade 36 (e.g. via track 44 including dove tail grooves formed on theinterior of blade 36) and inserting the distal end of the shim into thedisc space. In this manner, the posterior blade 36 will not moveposteriorly (towards nerve tissue located in the posterior portion ofthe psoas muscle). Instead, the blades 38 and 40 will move away from theposterior blade 36 to expand the access corridor. Additionally, nervemonitoring (including determining nerve proximity and optionallydirectionality) is preferably performed as each component of the accesssystem 26 is advanced through the psoas muscle, protecting the delicatenerve tissue running through the psoas, as described in the '949 patentand '668 application. Monitoring the proximity of nerves also allows theposterior blade 36 of the retractor assembly 34 to be positioned veryposterior (all the way back to the exiting nerve roots), thus exposing agreater portion of the disc space than would otherwise be safelyachievable. This inturn permits full removal of the disc andimplantation of a wider implant and the wider implant makes utilizationof the hyper-lordotic implant with a large lordotic angle (e.g. between20-40 degrees) more practical.

With the lateral access corridor formed (as pictured in FIG. 5) thetarget site may be prepped for insertion of the implant 10. Preparationof the disc space may include performing an annulotomy, removal of discmaterial, and abrasion of the endplates and instruments such asannulotomy knives, pituitaries, curettes, disc cutters, endplatescrapers may be used. Additionally, as discussed above, it may generallybe necessary to release the ALL in order to create enough flexibilitybetween the adjacent vertebrae (e.g. V1 and V2) to receive thehyper-lordotic implant 10. Unlike an anterior approach (where the greatvessels and other tissue lying anterior to the disc space is retractedduring the approach), when the target disc is approached laterally, thegreat vessels remain adjacent to the ALL along the anterior face of thespine. Thus, while cutting the ALL is generally simple and necessaryduring an anterior approach surgery, cutting the ALL during a lateralapproach surgery has typically been unnecessary and can be difficultbecause of the need to avoid damaging the great vessels. Accordingly,FIGS. 5-14 set forth various example embodiments of ALL resectinginstruments for safely releasing the ALL from a lateral approach.

FIGS. 5-8 illustrate one example ALL resector 50. The ALL resector 50includes a tissue retractor 52 and a sliding blade 68 and functions toboth sever the ALL and protect surrounding tissue (e.g. great vessels,nerves etc . . . ) from unwanted damage while the ALL is being severed.The tissue retractor 52 includes a handle 54, hollow shaft 56, and head58. The head 58 is curved, preferably such that the inside surface 60complements the curvature of the anterior aspects of the spinal targetsite. The head 58 may thus be positioned through the lateral accesscorridor to the spine and such that the curved interior surface 60nestles around the anterior curved anterior aspect of the spine. Theoutside surface 62 will form a barrier, protecting tissue along theanterior spine from inadvertent contact with the sliding blade when theALL is cut. Furthermore, the tissue retractor 52 can be furthermanipulated move tissue and further expose the anterior aspect of thetarget site. The hollow shaft 56 includes a central lumen 64 with anopening adjacent the head 58 and another opening at the opposing endsuch that the sliding blade 54 may travel through the shaft 56.

The sliding blade 68 includes a blade 70 that is secured to the distalend of an extender 72 by way of an attachment feature 74. The attachmentfeature 74 as shown is similar to known attachment features used forattaching a blade at the end of a scalpel. It will be appreciated thatany number of mechanisms may be used to attach blade 70 to extender 72.Blade 70 may be disposable and extender 72 may be reusable.Alternatively, both blade 70 and extender 72 may be reusable or both maybe disposable. The blade 70 includes a cutting edge 76 that, whenadvanced beyond the lumen 64 of shaft 56, cuts through tissue ormaterial situated adjacent the cutting edge 76.

The proximal end of the extender 72 includes a grip 78 that a user mayuse to manipulate the position of the sliding blade 40 relative to theshaft 56 and head 58. At least one stop feature 80 extends from theouter surface of the extender 72 which engages with a track 66 thatextends along a portion of the elongated shaft 56. The track 66 limitsthe longitudinal travel of the sliding blade 68 relative to the shaft 56so that the sliding blade 68 remains slidably mated to the tissueretractor 52 without becoming unassembled and such that the blade 70cannot extend beyond the protective head 58. Additionally, the stopfeature 80 restricts rotation of the sliding blade 68 relative to thetissue retractor 52.

FIGS. 9-8 illustrate another example embodiment of an ALL resector 82.The ALL resector 82 includes a handle 84 (for example, a T-handle)located at the proximal end of the elongated shaft 86 and a distal head88 for resecting the ALL. The distal head 88 includes distally extendingfirst and second fingers 90, 92, which form an opening 94 therebetween.First and second tapered surfaces 96, 98 which extend a distance fromthe elongated shaft 84 along the fingers 90, 92 enable the distal head88 to insert gently between tissue. As best shown in FIG. 11, the firstfinger 90 may be shorter in length than the second finger 92. However,the first and second finger 90, 92 may be provided in any number oflength configurations without departing from the scope of the presentinvention. By way of example, it has been contemplated that the firstfinger 14 may be completely removed. Alternatively, as pictured in FIG.12, the fingers 90 and 92 may be curved and have a more substantialwidth than shown in FIGS. 9-11. The curvature of the first and secondfingers allows the distal head 88 to follow closely along the anteriorside of the spine and/or along a curved spatula (not shown) positionedadjacent the anterior side of the vertebral body. Though not shown, auser may optionally insert a spatula along the anterior portion of theALL prior to inserting the ALL retractor 82. The spatula may serve asadditional protection between the delicate tissue anterior to the ALLand the cutting blade 97 of the ALL resector 82. With a spatula in placethe user may insert the distal head 88 such that it approaches thelateral side of the ALL and is guided along the inside edge of thespatula. By way of example, the spatula may be straight or curved tomatch the selected fingers of the distal head 88.

A cutting blade 97 is exposed between the first and second fingers 90,92 in the opening 17. A slot 99 formed along a side of the distal head88 allows a cutting blade 97 to be inserted and removed from the distalhead 88. Thus, the cutting blade 97 may be disposable and the remainderof the ALL resector 82 may be reusable. Alternatively, both cuttingblade 97 and remainder of the ALL resector 82 may be reusable or bothmay be disposable. In use, the ALL resector 82 is preferably positionedsuch that the second finger 92 is aligned along the anterior side of theALL and the first finger 90 is aligned along the posterior side of theALL, thus, at least partially bounding the ALL on either side. The ALLresector 82 is advanced forward so that the cutting blade 97 cutsthrough the ALL from one lateral edge to the other. As discussed above,the second finger 92 is preferably aligned along the anterior side ofthe ALL as the distal head 88 is advanced, thereby shielding the tissuelying anterior to the finger 92 (e.g. great vessels, etc . . . ) fromthe cutting blade 97. Furthermore, as the user advances the ALL resector82, the fingers 90, 92 may also act as a stabilizing guide.

Turning now to FIGS. 13-19, various embodiments of the hyper-lordoticimplant 10 are described. FIGS. 13-15, for example, illustrate anexample implant 110. Implant 110 may preferably be comprised of anysuitable non-bone composition having suitable radiolucentcharacteristics, including but not limited to polymer compositions (e.g.poly-ether-ether-ketone (PEEK) and/or poly-ether-ketone-ketone (PEKK))or any combination of PEEK and PEKK. Other materials such as forexample, metal, ceramics, and bone may also be utilized for the implant110. Implant 110 has a top surface 116 and bottom surface 118 forcontacting V1 and V2, anterior sidewall 112, posterior sidewall 114, andfront or leading side 120, and rear or trailing side 122. As discussed,the anterior sidewall 112 has a height greater than the posteriorsidewall 114 such that the top surface 116 and bottom surface 118converge towards each other in the posterior direction. By way ofexample, the top and bottom surfaces may converge at an angle between 20and 40 degrees. It is contemplated that variations of the implant 110may be simultaneously provided such that the user may select fromdifferent available ranges. For example, variations may be provided with20 degree, 30 degree, and 40 degree angles. The top and bottom surfacesmay be planar or provided as convex to better match the natural contoursof the vertebral end plates. The length of the implant 110 is such thatit may span from one lateral aspect of the disc space to the other,engaging the apophyseal ring on each side. By way of example, theimplant 110 may be provided with a length between 40 mm and 60.

Having been deposited in the disc space, the implant 110 facilitatesspinal fusion over time by maintaining the restored curvature as naturalbone growth occurs through and/or past the implant 10, resulting in theformation of a boney bridge extending between the adjacent vertebralbodies.

The implant 110 may be provided with any number of additional featuresfor promoting fusion, such as apertures 127 extending between the topand bottom surfaces 116-117 which allow a boney bridge to form throughthe implant 110. Various osteoinductive materials may be depositedwithin the apertures 127 and/or adjacent to the implant 110 to furtherfacilitate fusion. Such osteoinductive materials may be introducedbefore, during, or after the insertion of the exemplary spinal fusionimplant 110, and may include (but are not necessarily limited to)autologous bone harvested from the patient receiving the spinal fusionimplant, bone allograft, bone xenograft, any number of non-bone implants(e.g. ceramic, metallic, polymer), bone morphogenic protein, andbio-resorbable compositions, including but not limited to any of avariety of poly (D,L-lactide-co-glycolide) based polymers. Visualizationapertures 128 situated along the sidewalls, may aid in visualization atthe time of implantation and at subsequent clinical evaluations. Morespecifically, based on the generally radiolucent nature of the preferredembodiment of implant 110, the visualization apertures 128 provide theability to visualize the interior of the implant 110 during X-ray and/orother suitable imaging techniques. Further, the visualization apertures128 will provide an avenue for cellular migration to the exterior of theimplant 110. Thus the implant 110 will serve as additional scaffoldingfor bone fusion on the exterior of the implant 110.

The implant 110 also preferably includes anti-migration featuresdesigned to increase the friction between the implant 110 and theadjacent contacting surfaces of the vertebral bodies V1 and V2 so as toprohibit migration of the implant 110 after implantation. Suchanti-migration features may include ridges provided along the topsurface 116 and/or bottom surface 118. Additional anti-migrationfeatures may also include spike elements 124 disposed along the top andbottom surfaces.

Tapered surfaces 126 may be provide along the leading end 120 to helpfacilitate insertion of the implant 110. Additional instrumentation mayalso be used to help deploy the implant 110 into the disc space. By wayof example, the implant installation device shown and described indetail in the commonly owned and copending U.S. patent application Ser.No. 12/378,685, entitled “Implant Installation Assembly and RelatedMethods,” filed on Feb. 17, 2009, the entire contents of which isincorporated by reference herein, may be used to help distract the discspace and deposit the implant therein.

FIGS. 16-17 illustrate an implant 210 according to another exampleembodiment. The implant 210 share many similar features with the implant110 such that like feature are numbered alike and repeat discussion innot necessary. The implant 210 differs from the implant 110 in that atrailing side 212 is configured for fixed engagement to one of theadjacent vertebral bodies (i.e. V1 or V2) to supplement the antimigration features and ensure the hyper-lordotic implant is notprojected out of the disc space. Specifically, the implant 210 includesa tab 213 extending vertically above the top surface 116 and/or belowthe bottom surface 118. Tabs 213 facilitate fixation of the implant 210to the adjacent vertebrae. In the example shown in FIGS. 16-17, the tab213 extends past both the bottom and top surfaces 118 and 116,respectively. It will be appreciated, however, that the implant 210 mayinclude, without departing from the scope of the present invention andby way of example only, a tab 213 that extend solely in one direction.Additionally, multiple tabs 210 of various sizes and/or shapes may beused throughout a single implant 210 to facilitate implantation orfixation. In the illustrated example, the tab has a single fixationaperture 214 for enabling the engagement of a fixation anchor (notshown) within the vertebral bone to secure the placement of the implant.In use, when the implant 210 is positioned within the disc space, thetab 213 engages the exterior of the upper and lower vertebra and thefixation anchor may be driven into the side of either the upper or lowervertebra. One will appreciate that various locking mechanism may beutilized and positioned over or within the fixation aperture 214 toprevent the fixation anchor from unwanted disengagement with the implant210. For example, a suitable locking mechanism may be in the form of acanted coil disposed within the fixation aperture 214 or a screw thatmay be engaged to the trailing end 212 and cover all or a portion of thefixation aperture 214 after the fixation anchor positioned.

FIGS. 18-19 illustrate an implant 310 according to another exampleembodiment. The implant 310 shares many similar features with theimplants 110 and 110 such that like feature are numbered alike andrepeat discussion in not necessary. The implant 310 differs from theimplant 110 in that a trailing side 312 is configured for fixedengagement to one of the adjacent vertebral bodies (i.e. V1 or V2) tosupplement the anti migration features and ensure the hyper-lordoticimplant is not projected out of the disc space. Specifically, theimplant 310 includes a tab 313 extending vertically above the topsurface 116 and/or below the bottom surface 118. Tab 313 facilitatesfixation of the implant 310 to the adjacent vertebrae. Tab 313 extendspast both the bottom and top surfaces 118 and 116, respectively. It willbe appreciated, however, multiple tabs 310 of various sizes and/orshapes may be used throughout a single implant 310 to facilitateimplantation or fixation. The implant 310 differs from the implant 210in that the tab 213 has includes a pair of fixation apertures 214 forenabling the engagement of a pair fixation anchors (not shown) withinthe vertebral bone to secure the placement of the implant. In use, whenthe implant 310 is positioned within the disc space, the tab 313 engagesthe exterior of the upper and lower vertebra and a fixation anchor isdriven into the side of each of the upper or lower vertebra. One willappreciate that various locking mechanism may be utilized and positionedover or within the fixation apertures 314 to prevent the fixationanchors from unwanted disengagement with the implant 310. One will alsoappreciate that single locking mechanism may be used to cover bothfixation apertures 314, or, a separate locking mechanism may be used tocover each fixation aperture 314. Again, by way of example, a suitablelocking mechanism may be in the form of a canted coil disposed withineach fixation aperture 314 or a screw that may be engaged to thetrailing end 312 and cover all or a portion of each fixation aperture314 after the fixation anchors are positioned.

While this invention has been described in terms of a best mode forachieving this invention's objectives, it will be appreciated by thoseskilled in the art that variations may be accomplished in view of theseteachings without deviating from the spirit or scope of the invention.For example, particularly at L5-S1 where the pelvic bone makes a lateralaccess approach difficult, an antero-lateral approach similar to theapproach utilized during appendectomies may be utilized.

What is claimed is:
 1. A method for correcting sagittal imbalance of aspine, the method comprising: creating an operative corridor along alateral, trans-psoas path to a target site of the spine; preparing anintervertebral space at the target site of the spine, the intervertebralspace being at least partially defined by an anterior aspect, aposterior aspect, and opposing first and second lateral aspects;advancing a tissue retractor through the operative corridor along thelateral, trans-psoas path to a protective position in which a protectivehead of the tissue retractor is positioned between an AnteriorLongitudinal Ligament (ALL) and anterior vasculature; and advancing acutting blade along the tissue retractor protective head and severingthe Anterior Longitudinal Ligament (ALL) with the cutting blade.
 2. Themethod of claim 1, subsequent to advancing the cutting blade along thealong the tissue retractor protective head and severing the AnteriorLongitudinal Ligament (ALL) with the cutting blade, further comprisingadvancing and intervertebral implant through the operative corridoralong the lateral, trans-psoas path.
 3. The method of claim 2 furthercomprising depositing the intervertebral implant into the intervertebraldisc space.
 4. The method of claim 3 further comprising anchoring theimplant to at least one of a first vertebra and a second vertebra. 5.The method of claim 4, wherein the intervertebral implant proximal endincludes an extension tab that abuts a lateral aspect of at least one ofthe first vertebra and second vertebra, the extension tab including atleast one aperture that receives a fixation anchor therethrough, whereinthe step of anchoring the implant comprises advancing an anchor throughthe at least one aperture into one of the first and second vertebra. 6.The method of claim 5, wherein the extension tab includes an upperportion including a first aperture that abuts a lateral aspect of firstvertebra and a lower portion including a second aperture that abuts alateral aspect of the second vertebra, and wherein the step of anchoringthe implant comprises advancing an anchor through the first apertureinto the first vertebra and advancing a second anchor through the secondaperture into second vertebra.
 7. The method of claim 6, wherein theintervertebral implant is a fusion implant and includes at least onefusion aperture opening in the upper surface and lower surface to permitbone growth between the first vertebra and second vertebra.
 8. Themethod of claim 1, wherein the tissue retractor protective head includesan inner surface that faces the ALL and an outer surface that that facesthe anterior vasculature when the tissue retractor is in the protectiveposition.
 9. The method of claim 1, wherein the tissue retractorprotective head includes a distal end that is curved around the anterioraspect of the target site and protects the anterior aspect of the targetsite from the cutting blade.
 10. The method of claim 1, wherein thetissue retractor includes a shaft extending from the protective head anda handle extending from the shaft.
 11. The method of claim 10, whereinthe shaft is hollow and the cutting blade travels through the hollowshaft.
 12. The method of claim 1, wherein the cutting blade is situatedon a distal end of an extender.
 13. The method of claim 1, wherein thecutting blade is situated on a distal end of an extender between a firstand a second finger.
 14. The method of claim 13, wherein the secondfinger curves along an anterior side of the ALL as the distal head isadvanced, thereby shielding the tissue lying anterior to the secondfinger from the cutting blade.
 15. The method of claim 13, wherein thecutting blade is disposable and the extender is reusable.
 16. The methodof claim 1, wherein creating the operative corridor along the lateral,trans-psoas path the access system comprises using at least one dilatorand a retractor that slides over the at least one dilator in a firstconfiguration, and there after adjusts to a second configuration toenlarge the operative corridor.
 17. A method for correcting sagittalimbalance of a spine, the method comprising: creating an operativecorridor along a lateral, trans-psoas path to a target site of thespine; preparing an intervertebral space at the target site of thespine, the intervertebral space being at least partially defined by ananterior aspect, a posterior aspect, and opposing first and secondlateral aspects; advancing a tissue retractor through the operativecorridor along the lateral, trans-psoas path to a protective position inwhich a protective head of the tissue retractor is positioned between anAnterior Longitudinal Ligament (ALL) and anterior vasculature, whereinthe protective head of the tissue retractor curves to complementanterior curvature of the target site of the spine; and advancing acutting blade along the tissue retractor protective head and severingthe Anterior Longitudinal Ligament (ALL) with the cutting blade, whereinthe cutting blade does not extend beyond the protective head.
 18. Themethod of claim 17, wherein creating the operative corridor along thelateral, trans-psoas path the access system comprises using at least onedilator and a retractor that slides over the at least one dilator in afirst configuration, and there after adjusts to a second configurationto enlarge the operative corridor.
 19. The method of claim 17,subsequent to advancing the cutting blade along the along the tissueretractor protective head and severing the Anterior LongitudinalLigament (ALL) with the cutting blade, further comprising advancing andintervertebral implant through the operative corridor along the lateral,trans-psoas path.
 20. The method of claim 17 further comprisingdepositing the intervertebral implant into the intervertebral discspace.